fgets problem

**belhifet** · 11-26-2006

I have the following code:

Code:

#include <stdio.h>

#define N 2

int main()
{


	int A[N][N];
	int i,j;
	char text[100];

	
	
	printf("input\n"); 
	for (i=0;i<N;i++)
		for (j=0;j<N;j++)
		{
			printf("element %d,%d ",i,j);
			scanf("%d",&A[i][j]);
		}
	printf("Input text:\n");
	fgets(text,40,stdin);
	printf("%s",text);
return 0;
}

The output is:
$./a.out
input
element 0,0 1
element 0,1 2
element 1,0 3
element 1,1 4
Input text:

$

The problem is that it terminates before it reads my string.
What should I change in order to make it work?

**ZuK** · 11-26-2006

scanf and fgets don't mix very well.
scanf leaves the terminating '\n' in the input buffer. the following fgets finds the '\n' and returns an empty string.
Kurt

**vart** · 11-26-2006

after you enter the number '\n' symbol is left in the input stream, next scanf ignores it, but fgets does not.

So it reads that left symbol in to the text array and then - prints it

**belhifet** · 11-26-2006

Yes, but what's the solution to this problem?
I need to use scanf and fgets.
Is there a way to remove the terminating '\n' from the input buffer?

Which functions could I have used alternatively?

**ZuK** · 11-26-2006

One solution could be to add another fgets statement or empty the buffer some other way.
Kurt

**belhifet** · 11-26-2006

ZuK I already tried the additional fgets, but it appears weird that way.

Anyone know how to empty the buffer in another way?

**ZuK** · 11-26-2006

Code:

 int ch;
  do
    ch = fgetc ( stdin ); 
  while ( ch != EOF && ch != '\n' );

Would help.
Kurt

**vart** · 11-26-2006

Anyone know how to empty the buffer in another way?

you can remove scanf and use pair
fgets/sscanf or fgets/strtol

in this case there will be no mix of fgets/scanf

**ssharish2005** · 11-26-2006

Code:

void clear_buffer()
{
    int ch;
    
    while((ch = getchar()) != EOF && ch != '\n');
}

ssharish2005

**dhanulakshmi** · 11-29-2006

use _fpurge or _fflush to remove \n from the buffer

**jeremy75** · 11-29-2006

i suggest you

replace this

scanf("%d",&A[i][j]);
=>
scanf("%d%c",&A[i][j]);

**vart** · 11-29-2006

scanf("%d%c",&A[i][j]); - you ask to read 2 values providing space only for one... the character will be written somewhere on the stack...

**Salem** · 11-29-2006

> use _fpurge or _fflush to remove \n from the buffer
Please don't suggest non-standard functions which don't solve the problem for everyone.

> scanf("%d%c",&A[i][j]);
Which fails just as miserably if the user types a space after the last digit entered.

> I need to use scanf and fgets.
You mean something else like scanf is OK if it works in a similar manner?
Or is this an exercise in understanding that scanf() and fgets() don't play together?

For example, what about this for you loop

Code:

printf("element %d,%d ",i,j);
fflush( stdout );
if ( fgets( text, sizeof text, stdin ) != NULL ) {
  if ( sscanf( text, "%d",&A[i][j]) == 1 ) {
  } else {
    // error message
  }
}

No scanf() to muck up the input stream, so the final fgets() will do the right thing unless the user is deliberately out to try and buffer overflow attack your code (in which case it's their problem).

> fgets(text,40,stdin);
It's exceedingly unwise to guess at the buffer size, even if you happen to guess smaller.
fgets(text, sizeof text,stdin);

**dwks** · 11-29-2006

Originally Posted by vart

scanf("%d%c",&A[i][j]); - you ask to read 2 values providing space only for one... the character will be written somewhere on the stack...

Assuming you don't mind it failing miserably as Salem mentioned, you can get scanf() to skip format specifiers with a * (in printf a * does something different). %*X

**Salem** · 11-29-2006

Learning the whole of C (except for scanf), and learning scanf() takes about the same amount of time.

All those ways to use it, and all those ways to louse it up as well.

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